Multiple lighting level ballast for fluorescent lamps

ABSTRACT

A ballast for starting and operating rapid-start fluorescent lamps includes a switch coupled to the running capacitor means in the ballast circuit. The switch can be selectively operated to a number of positions for varying the value of capacitance in circuit with the transformer and rapid-start lamps. A variation in the capacitor reactance varies the impedance of the series circuit thus varying the current in the lamps thus causing a change in the light level produced by the lamps.

United States Patent 191 Crawford et al.

[4 1 Oct. 7, 1975 MULTIPLE LIGHTING LEVEL BALLAST FOR FLUORESCENT LAMPS [75] Inventors: Joseph A. Crawford, Chicago; Fred Abrahams, Skokie, both of II].

[73] Assignee: Advance Transformer Company,

Chicago, Ill.

22 Filed: Aug. 5, 1974 21 Appl.No.:494,413

[52] US. Cl. 315/240; 315/94; 315/187; 315/227 R; 315/DIG. 4 [51] Int. Cl. H05B 41/40; HOSB 41/14 [58] Field of Search 315/94, 187, 227 R, 239, 315/240, 244, 247, 278, 311, DIG. 4, DIG. 5

[56] References Cited UNITED STATES PATENTS 3,323,013 5/1967 Lord 315/187 Primary Examiner.lames W. Lawrence Assistant ExaminerE. R. LaRoche Attorney, Agent, or FirmSilverman & Cass, Ltd.

[ 5 7 ABSTRACT A ballast for starting and operating rapid-start fluorescent lamps includes a switch coupled to the running capacitor means in the ballast circuit. The switch can be selectively operated to a number of positions for varying the value of capacitance in circuit with the transformer and rapid-start lamps. A variation in the capacitor reactance varies the impedance of the series circuit thus varying the current in the lamps thus causing a change in the light level produced by the lamps.

9 Claims, 2 Drawing Figures US. Patent Oct. 7,1975

F IG.

|ll| ll lllllllllllllll I FIGZ PRIOR ART MULTIPLE LIGHTING LEVEL BALLAST FOR FLUORESCENT LAIVIPS BACKGROUND OF THE INVENTION This invention relates generally to apparatus for starting and operating fluorescent lamps for lighting, and more particularly is concerned with such apparatus intended for use in providing multiple lighting levels.

In recent years, fluorescent lighting has increased in. popularity for commercial, industrial and residential applications. In all such applicationsthe fluoroescent lighting usually provides a high level, even lighting which is excellent for working, reading or recreation. In many situations, however, this high level uniform lighting is not necessary and sometimes it is even undesirable. In the past, in order to reduce the light level and still provide uniform fluorescent type illumination, switching was provided for turning on or off alternate groups or banks of lamps. This can be expensive and potentially wasteful because it results in non-uniform lighting with dark areas or multiple ballast usage to provide uniform lighting.

Fluorescent dimmers have been developed which can control the current and voltage of the lamps in a fluorescent fixture to vary the light level of the fixtures. These dimmers are complex in structure and very expensive. Generally, they are designed to operate only a few fixtures at one time.

SUMMARY OF THE INVENTION In practicing this invention, a ballast is provided for starting and operating at least one rapid-start fluorescent lamp. The ballast includes a high leakage reactance transformer coupled in series-circuit relationship with the fluorescent lamp and a capacitor. This capacitor acts to provide a leading current in the circuit. A switch is coupled to the capacitor for varying the capacitive reactance thereof to change the lighting level of the lamp.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of the ballast apparatus of this invention in circuit with a pair of seriesconnected rapid-start fluorescent lamps; and

FIG. 2 is a schematic diagram of the prior art apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 2 shows the prior art series-sequence-start circuit for rapid start fluorescent lamps. The prior art circuit will not be discussed in detail as all elements thereof and the operation thereof are discussed in connection with FIG. 1.

Referring to FIG. 1, the series-sequence-start ballast includes a high leakage reactance transformer 12 having a magnetic core 14, a primary winding P, a secondary winding S, and magnetic shunts 16. Three filament windings F F and F are closely coupled with the primary winding P on magnetic core 14. Primary winding P and secondary winding S are seriesconnected forming an autotransformer configuration. Input leads 18 and 20 couple primary winding P across a source of A.C. voltage 8,.

A pair of rapid-start fluorescent lamps designated L and L respectively is series-connected and the lamps are designated with a numeric subscript in the order of ignition. Primary winding P and secondary winding S are connected in series additive arrangement across lamps L, and L A grounded conductive plate 21, which in most applications is the fixture in which the lamps and ballasts are mounted,'is positioned in close proximity to lamps L and L so as to be capacitively coupled therewith. Conductive plate 21 is normally necessary for proper starting of the lamps.

Lamp L has two filaments 22 and 24. One side of filament'22 is connected via conductor 26 to the junction of primary winding P and filament winding F The other side of filament 22 is coupled via conductor 28 to the second side of filament winding F Rapid-start fluorescent lamp L includes a filament 30 and filament 32. Ends of filament 30 are respectively connected to the ends of filament 24 of lamp L .via conductors 33 and 34. A conductor 36 connects conductor 33 to one end of filament winding F and a conductor 38 connects conductor 34 to the other end of filament winding F Filament 32 is connected across filament winding F via conductors 40 and 42.

A capacitor C, has oneterminal connected to conductor 38 and the other terminal connected to conductor 42 so that capacitor C is in parallel with lamp L Capacitor C is commonly known in the art as the starting condenser. Capacitors C and C are series- .connected from one end of secondary winding S to conductor 42 so that capacitors C and C primary winding P, secondary winding S and lamps L and L are all in series-circuit relationship. Capacitors C and C may be considered together as the series condenser to provide a leading current during operation of the lamps.

A switch SW is provided having outer contacts 46 and 48, a center contact 50 and a'movable center arm 52 which can be selectively connected to any one of contacts 46, 48 or 50. Movable center arm 52 is connected via a conductor 54 to the junction of capacitors C and C Outer contact 46 is connected to the secend terminal of capacitor C which is connected to one end of secondary winding S and contact 50 is connected to the second terminal of capacitor C which is connected to conductor 42. With contact arm 52 con nected to contact 46, capacitor C is short-circuited and the total series capacitance is provided by capacitor C With movable arm 52 in contact with contact 48, both capacitors C and C in series, are in seriescircuit relationship with the transformer and fluorescent lamps and the total capacitance is the reciprocal of the sum of the reciprocals of 'the two capacitors. With contact arm 52 in contact with terminal 50 capacitor C is shorted and capacitor C only is in seriescircuit relationship with the transformer and fluorescent lamps. Although switch SW can be mounted on a wall, it is most conveniently mounted directly on the fixture containing the lamps and ballast with the conductors brought out of the ballast to switch SW The mounting of switch SW, to fixture 21 is shown schematically in FIG. 1 via the dotted line connection between switch SW, and fixture 21.

In operation, when leads l8 and 20 are connected to the source of A.C. voltage S a high voltage is induced in secondary winding S. The combined voltages across primary winding P and secondary winding S appear across only lamp L i.e., from conductor 26 to conductor 42 since capacitor C and capacitors C and C have practically no effect on the circuit when power is initially applied and no current flows in the secondary circuit. Consequently, the relatively large voltage appearing across the lamp L, causes it to ignite. As soon as current begins to flow through lamp L current flows through capacitor C which now develops a voltage there-across. The voltage across capacitor C, will increase to a point Where it is sufficient to ignite lamp L Current flowing in lamp L now by-passes eon denser C because of its lower impedance. Thereafter, both lamps are supplied with current in series through capacitors C and C primary winding P and secondary winding S. Capacitors C and C as noted above, act to provide the necessary lead current in the secondary circuit and to some extent affect the power factor of the circuit.

It should be noted that in ballast circuits for fluorescent lamps, a perfect power factor would exist when the primary reactive current neutralizes the leading secondary current provided by capacitor C and C For this reason in modern ballast circuits of this type a leading secondary current is preferred. This occurs when the net reactance provided in the series circuit is capacitive. It is the capacitive reactance in the series circuit which is varied in the instant invention so that irrespective of which condensers are switched into the circuit the net reactance will still be capacitive. This particular circuit feature and operation are employed via selective operation of switch SW Switch SW is operative to vary the value of capacitance in seriescircuit relation with transformer 12 and lamps L and L The variation in value of capacitive reactance causes a variation in the circuit impedance which causes a variation in the light level produced by lamps L, and L In the preferred embodiment, capacitor C is 3.95 rnicrofarads and capacitor C is 1.9 rnicrofards. In position I with center arm 52 in contact with terminal 46 maximum illumination is provided by lamps I. and L because the capacitive reactance furnished by the capacitance C [3.95 mfd.] is minimum and current flow is maximum. In position 2 with movable arm 52 in contact with terminal 50, only the smaller capacitor C is in series-circuit relationship and the illumination provided by lamps L and L is at the level intermediate that of positions 1 and 3 which in the preferred embodiment is 50 percent of maximum. At this condition the level of capacitive reactance is intermediate. In position 3 with movable arm 52 in contact with terminal 48, the total series capacitance is minimized, capacitive reactance is greatest and therefore the least current flows. This results in the lowest light level output which in this embodiment is percent of maximum.

It must be appreciated that the total capacitive reactance X of the secondary circuit must always be greater than the total inductive reactance X of the circuit for the current to be leading. Thus, when condenser C is in the circuit and maximum current flows an increase in capacitive reactance (decrease in capacitance) must result in a decrease in current. The circuit is therefore always leading.

The switch SW is shown as a three-position toggle type switch with position 3 open permitting a natural sequence from high to medium to low illumination. Switch SW can also be a three-position toggle type in which there is only one contact to the movable arm and two stationary contacts. If this type switch is employed the center position, which would be for the lowest light level, would be detented for properly locating the toggle. The two stationary outer contacts would be connected so as to provide the high and low light levels.

While the present invention has been described by reference to a specific example, it is to be understood that modifications may be made by those skilled in the art without actually departing from the invention. For example, this invention may be employed with equal advantage in a single lamp rapid start circuit or in a rapid start circuit employing more than two lamps. A high leakage reactance isolated primary and secondary transformer also can be provided in place of autotransformer 12 in certain embodiments. It is, therefore, intended that the appended claims cover all variations that fall within the scope and spirit of the invention.

What it is desired to secure by Letters Patent of the United States is:

l. A ballast apparatus for starting and operating at least one fluorescent lamp comprising:

a high leakage reactance transformer having a primary winding and a secondary winding;

capacitive reactance means including a first number of series connected capacitors, said first number being greater than one, in series-circuit relationship with said transformer and having a capacitive reactance value to cause a leading current to flow therethrough;

means including electrical leads for extending connections from said transformer and capacitive reactance means to the lamp to form a series circuit therewith when connected thereto; and

switching means coupled to said first number of capacitive reactance means and having a second number of selectable switch positions, said second number being one more than said first number, the fluorescent light level being selectively variable to any one of a second number of light levels when connected as aforesaid whereby the number of light levels which may be obtained is one greater than the number of said series connected capacitors.

2. The ballast of claim 1 wherein said capacitive reactance means include first and second series-connected capacitors, and said switch means include a threeposition switch with a center arm movable to a first and second position to contact first and second contacts respectively, and a third position without electrical connection to either capacitor, said center arm being coupled to the junction of said first and second seriesconnected capacitors, said first contact being coupled to a second end of said first capacitor and said second contact being coupled to a second end of said second capacitor whereby one or the other of said first and second. capacitors is short-circuited by said switch means in one of said first and second positions.

3. The ballast of claim 1 wherein said primary and secondary windings are in series-circuit relation forming an autotransformer.

4. The ballast of claim 1 wherein said first number is two and said switch means are operative to selectively couple both, one or the other of said capacitors in series-circuit relationship with said transformer.

5. The ballast of claim 4 wherein said switch means comprise a three-position switch.

6. A ballast apparatus for starting and operating at least a pair of fluorescent lamps wherein the lamps are cuit to cause a leading current to flow there-' through; and

switching means arranged in connection with said second capacitive reactance means and operative selectively to couple both, one or the other of said first and second series coupled capacitors in seriescircuit relationship with said autotransformer whereby the fluorescent light level is varied to any one of three different conditions depending upon the coupling.

7. The ballast of claim 6 wherein said switch means include a three-position switch having a center arm movable to a first and second position to contact first and second contacts respectively and a third position, said center arm being coupled to the junction of said first and second series-connected capacitors, said first contact being coupled to a second end of said first capacitor and said second contact being coupled to a second end of said second capacitor.

8. The ballast of claim 6 wherein said primary and secondary windings are coupled in series with one another and said second capacitive reactance means, said primary winding being coupled to a source of alternating current.

9. The ballast of claim 6 wherein said switch means are a three-position switch. 

1. A ballast apparatus for starting and operating at least one fluorescent lamp comprising: a high leakage reactance transformer having a primary winding and a secondary winding; capacitive reactance means including a first number of series connected capacitors, said first number being greater than one, in series-circuit relationship with said transformer and having a capacitive reactance value to cause a leading current to flow therethrough; means including electrical leads for extending connections from said transformer and capacitive reactance means to the lamp to form a series circuit therewith when connected thereto; and switching means coupled to said first number of capacitive reactance means and having a second number of selectable switch positions, said second number being one more than said first number, the fluorescent light level being selectively variable to any one of a second number of light levels when connected as aforesaid whereby the number of light levels which may be obtained is one greater than the number of said series capacitors.
 2. The ballast of claim 1 wherein said capacitive reactance means include first and second series-connected capacitors, and said switch means include a three-position switch with a center arm movable to a first and second position to contact first and second contacts respectively, and a third position without electrical connection to either capacitor, said center arm being coupled to the junction of said first and second series-connected capacitors, said first contact being coupled to a second end of said first capacitor and said second contact being coupled to a second end of said second capacitor whereby one or the other of said first and second capacitors is short-circuited by said switch means in one of said first and second positions.
 3. The ballast of claim 1 wherein said primary and secondary windings are in series-circuit relation forming an autotransformer.
 4. The ballast of claim 1 wherein said first number is two and said switch means are operative to selectively couple both, one or the other of said capacitors in series-circuit relationship with said transformer.
 5. The ballast of claim 4 wherein said switch means comprise a three-position switch.
 6. A ballast apparatus for starting and operating at least a pair of fluorescent lamps wherein the lamps are arranged in series-circuit relation including in combination: first capacitive reactance means comprising a starting capacitor coupled in parallel with one of said fluorescent lamps; a high reactance transformer having a primary and secondary winding forming an autotransformer configuration; second capactive reactance means including first and second series coupled capacitors in series-circuit relationship with said autotransformer and adapted to be coupled in series-circuit relationship with said fluorescent lamps, said second capacitive reactance means having a capacitive reactance of such value related to the inductive reactance of the circuit to cause a leading current to flow therethrough; and switching means arranged in connection with said second capacitive reactance means and operative selectively to couple both, one or the other of said first and second series coupled capacitors in seriEs-circuit relationship with said autotransformer whereby the fluorescent light level is varied to any one of three different conditions depending upon the coupling.
 7. The ballast of claim 6 wherein said switch means include a three-position switch having a center arm movable to a first and second position to contact first and second contacts respectively and a third position, said center arm being coupled to the junction of said first and second series-connected capacitors, said first contact being coupled to a second end of said first capacitor and said second contact being coupled to a second end of said second capacitor.
 8. The ballast of claim 6 wherein said primary and secondary windings are coupled in series with one another and said second capacitive reactance means, said primary winding being coupled to a source of alternating current.
 9. The ballast of claim 6 wherein said switch means are a three-position switch. 